Well, Merriam-Webster is no help:
diner: a restaurant usually resembling a dining car in shape
restaurant: a business establishment where meals or refreshments may be purchased
So, still, most diners are NOT shaped like railroad cars anymore.
I guess a diner is a type of restaurant?
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Dave
“A person has the right to keep and bear arms for the defense of self, family, home and State, and for hunting and recreational use.” [Delaware Constitution, Article I, § 20 Right to keep and bear arms]